Abstract:
The invention relates to a method of treating liquid flows at a chemical pulp mill comprising at least an alkaline cooking process utilizing cooking liquor for producing pulp, brown stock treatment with essentially closed liquid cycles, a pulp bleaching plant using ECF-bleaching wherein chloride- containing effluents are generated, a chemical recovery plant comprising a causticizing plant and chemical recovery boiler plant, and effluent purification. A characteristic feature of the method is that chloride-containing effluents of the bleaching plant are introduced to the effluent purification where they are treated for decreasing the organic matter content thereof, at least 20 % of the purified effluent is led back to a pulp mill process, purified effluent is used in at least one stage of causticizing as raw water source so that the chloride-containing liquid formed in the process stage is a weak white liquor fraction that is led to the recovery boiler plant as a smelt dissolving liquid component and therefrom further via regeneration of cooking liquor, pulp cooking and pulp washing as a waste liquor component to evaporation, wherefrom the concentrated waste liquor is led for treatment into a recovery boiler process, wherein a separation process for chlorides is arranged in order to control the chloride-level of the liquor cycle.
Abstract:
The invention relates to a method of treating liquid flows at a chemical pulp mill comprising at least an alkaline cooking process utilizing cooking liquor for producing pulp, brown stock treatment with essentially closed liquid cycles, a pulp bleaching plant using ECF-bleaching wherein chloride- containing effluents are generated, a chemical recovery plant comprising a causticizing plant and chemical recovery boiler plant, and effluent purification. A characteristic feature of the method is that chloride-containing effluents of the bleaching plant are introduced to the effluent purification where they are treated for decreasing the organic matter content thereof, at least 20 % of the purified effluent is led back to a pulp mill process, purified effluent is used in at least one stage of causticizing as raw water source so that the chloride-containing liquid formed in the process stage is a weak white liquor fraction that is led to the recovery boiler plant as a smelt dissolving liquid component and therefrom further via regeneration of cooking liquor, pulp cooking and pulp washing as a waste liquor component to evaporation, wherefrom the concentrated waste liquor is led for treatment into a recovery boiler process, wherein a separation process for chlorides is arranged in order to control the chloride-level of the liquor cycle.
Abstract:
The present invention relates to a method for treating pulp at a chemical pulping plant comprising at least a pulp bleaching plant using elementary chlorine free bleaching and having at least one chlorine dioxide stage, and wherein chloride-containing effluents are formed, a chemical recovery plant comprising a black liquor evaporation plant and a chemical recovery boiler plant, and effluent purification. An object of the present invention is to offer a method for utilizing liquid flows generated at a chemical pulp mill in an advantageous objet and for efficiently circulating them and minimizing the emissions from the mill. A characteristic feature of the method is that chloride-containing bleaching plant effluents are led to effluent purification, where they are treated in order to decrease the organic matter content thereof, that purified effluent is led back to a chemical pulp mill process, so that at least 20 % of the liquid used for brown stock washing is purified effluent and that condensates originating from the evaporation plant are used in the amount of at least 1 m 3 /adt pulp as washing or dilution water of the bleaching for reducing the total amount of effluent, and that a separation process for chlorides is arranged at the chemical recovery boiler plant for decreasing the chloride level of the chemical cycle.
Abstract:
The present invention relates to a method of treating pulp and an apparatus applying the method. The method and the apparatus according to the invention are especially suitable for the bleaching of medium consistency pulp when bleaching stages of various temperatures are used. It is characteristic of the invention to treat pulp in connection with chemical pulp manufacturing process in such a manner that pulp is allowed to flow prior to the bleaching reactor, in the reactor itself, and/or thereafter at a rate of less than 5 m/s through an indirect heat exchanger, for changing the pulp temperature over 5 DEG C, preferably over 10 DEG C.
Abstract:
The present invention relates to a method and apparatus, the purpose of which is to separate more efficiently than hitherto liquid from liquid/fiber suspension by dividing the suspension into two portions, of which one includes mainly liquid and the other both fibers and liquid. The method and apparatus in accordance with the invention may especially well be applied to the thickening of low consistency (0.5 - 5 %) fiber suspensions in pulp and paper industry. The thickening method in accordance with the invention is characterized in that micro turbulence is generated on the filter surface by means of the filter surface, by which thickened fiber matting on the surface is dispersed or the generation thereof is prevented. The thickening apparatus in accordance with the present invention is again characterized in that unevennesses (24) are arranged on the filter surface (23), which together with the kinetic speed of the fiber suspension generate micro turbulence of high intensity, by which the fiber matting tending to form in close proximity to the filter surface (23) is dispersed to optimize the thickening process.
Abstract:
The present invention relates to a method for treating liquid flows at a chemical pulp mill comprising at least an alkaline cooking process for producing pulp, brown stock treatment with essentially closed liquid cycles, a pulp bleaching plant using ECF-bleaching, a chemical recovery plant comprising a chemical recovery boiler, and effluent purification. Chloride-containing bleaching plant effluents are led to the effluent purification, where they are treated in order to decrease the organic matter content thereof. At least 20 % of the purified effluent is returned to a pulp mill process and purified effluent is used in a last washing stage included in brown stock treatment. In the brown stock treatment the liquid flow is passed counter-currently to evaporation, wherefrom it is led for treatment to a recovery boiler process, wherein a separation process for chlorides is arranged for controlling the chloride level of the liquor cycle.
Abstract:
The present invention relates to a method of treating pulp in connection with the bleaching of chemical pulp, said method comprising treating of the pulp in at least an ozone, chlorine dioxide or alkali phase and thereafter washing of the pulp in a washing device having an E 10 value of at least 3, whereby washing liquid is introduced into the washing device countercurrently in relation to the pulp and filtrate is discharged from the washing device. At first the pulp is washed in the washing device so that the washing liquid is filtrate obtained from the washing device itself and the amount of thus circulated washing liquid is 1.5 - 3.5 t/adt pulp, whereafter the pulp is washed with liquid introduced from outside the washing device, the amount of said liquid being such that the dilution factor in the latter wash is less than 1 t/adt and that the total amount of washing liquid used in the washing device is such that the dilution factor is more than 0 t/adt.
Abstract:
The present invention relates to a method of bleaching sulfate cellulose pulp to a brightness of at least ISO 85 by using at least two of the following bleaching chemicals: oxygen, ozone, and peroxide. Characteristic features of the invention are that the pulp is digested; subjected to a heavy metals removal treatment with at least one of the following treatment agents or methods: acidification, EDTA, and DTPA; delignified in a pressurized two-step oxygen stage; and bleached at least in one acid peroxide stage.
Abstract:
The present invention relates to a method of treating and utilizing liquid flows at a chemical pulp mill. The method comprises at least the following stages: a) chemical pulp is produced in an alkaline cooking process, b) the brown stock generated in the cooking is treated, said treatment comprising washing of the stock and preferably oxygen delignification and subsequent washing of the stock, c) a bleaching process for the brown stock, the bleaching sequence comprising at least one stage using chlorine dioxide and additionally at least one oxidizing bleaching stage and having at least two washing stages for treating the stock with liquids and for producing filtrates, and d) filtrates from stage c) are purified at an effluent treatment plant of the chemical pulp mill, which comprises at least biological treatment, for obtaining purified effluent. The method further comprises a stage e), where the purified effluent with a color of 200 mg/l (R color) or more and a COD value of over 150 mg/l is used as pulp treatment liquid in stage c).
Abstract:
The present invention relates to a method in connection with washing of pulp at a chemical pulp mill comprising at least an alkaline cooking process utilizing cooking liquor for producing pulp, brown stock treatment with essentially closed liquid cycles, in which the last washing device is a washing device based on pressing of pulp, a press or a washing press, a pulp bleaching plant using ECF- bleaching, wherein chloride-containing effluents are formed, a chemical recovery plant and effluent purification. An object of the present invention is to offer a method for utilizing liquid flows generated at a chemical pulp mill in an advantageous object and for efficiently circulating them without disturbing the main process and minimizing the emissions from the mill. A characteristic feature of the invention is that purified effluent in the amount of at least 1 m3/adt pulp is introduced into the dilution after the press or washing press, whereby the effluent is passed from the dilution into the first process stage of the bleaching.